A known gas sensor for detecting the concentration of oxygen or NOx in exhaust gas of an automobile or the like has a plate-like sensor element which uses solid electrolyte.
In a widely used gas sensor of such a type, a plurality of electrode pads are provided on the outer surface of a rear end portion of the plate-like sensor element, and metal terminal members are brought into electrical contact with the electrode pads so as to output a sensor output signal from the sensor element and supply electricity to a heater stacked on the sensor element (Japanese Patent Application Laid-Open (kokai) No. 2012-230076 (FIGS. 3 and 4)).
As shown in FIG. 14, each metal terminal member 200 is formed from a metal plate through, for example, cutting and raising, and has a strip-like shape. The metal terminal member 200 has a folded-back portion 202 whose distal end portion is folded back toward a sensor element (not shown) for elastic contact with an electrode pad of the sensor element, and a crimp portion 204 to which a distal end of a lead wire 146 is fixed by means of crimping.
The metal terminal member 200 also has a locking portion 206 which protrudes in a direction opposite the folded-back portion 202 thereof and has an L-shaped cross section. The locking portion 206 is accommodated in an L-shaped groove 300g formed on the forward side of a separator hole 300h of a separator 300. The locking portion 206 comes into locking engagement with a forward-facing surface 300s of the groove 300g, whereby the metal terminal member 200 is held in the separator 300.
Notably, in the example of FIG. 14, the metal terminal member 200 is rotated counterclockwise by about 90 degrees, and the locking portion 206 is inserted into the upper right groove 300g. A total of four such metal terminal members 200 are individually accommodated in different grooves 300g. 
The lead wire 146 is connected (crimped) to the metal terminal member 200 as follows. First, the lead wire 146 is inserted into the separator hole 300h of the separator 300 from the rear side of the separator 300 and is pulled out toward the forward F side of the separator 300. Next, a distal end portion of the lead wire 146 is fixed, by means of crimping, to the crimp portion 204 of the metal terminal member 200 disposed on the forward side of the separator 300, whereby the lead wire 146 is connected to the metal terminal member 200.
Then, when the lead wire 146 is pulled toward the rear R side such that the lead wire 146 is pulled out rearward of the separator 300, the metal terminal member 200 connected to the lead wire 146 is also pulled toward the rear R side. As a result, the locking portion 206 is accommodated in the groove 300g and comes into locking engagement with the forward-facing surface 300s of the groove 300g, thereby preventing rearward coming off of the metal terminal member 200. In this manner, the metal terminal member 200 is incorporated into the separator 300.